With Cutler out, Jimmy Clausen will take over as the Bears' starting quarterback.

Earlier Monday, Bears coach John Fox confirmed that medical tests showed that Jay Cutler suffered a strained hamstring in Chicago's 48-23 loss to the Arizona Cardinals but did not announce a timetable for Cutler's return.

Cutler injured his hamstring while trying to tackle Cardinals safety Tony Jefferson, who intercepted a pass intended for Martellus Bennett deep in Chicago territory. Jefferson scored on the play to give the Cardinals a 28-14 lead with 2:59 remaining in the second quarter.

Clausen entered the game on the next possession and finished 14-of-23 for 121 yards, with one interception and a passer rating of 56.6.

"As I mentioned yesterday," Fox said, "considering the circumstances and his preparation reps and getting ready to play Arizona, most backups are not getting all those reps regardless of the position. I think at the quarterback position it's a little tougher because you have to be in tune to everybody else completely. But I think all in all, [Clausen] did OK."

Fox said the Bears have not decided whether they will sign another quarterback.

"Think we'll evaluate that, and we have all the way until Saturday to do anything like that," he said.

The club could elevate second-year quarterback David Fales from the practice squad to the active roster. A 2014 sixth-round draft choice, Fales spent four weeks last year on the Bears' 53-man roster but never appeared in a game. He was on the active roster before Week 1 against Green Bay but was inactive on game day.

Bears linebacker Jared Allen said Cutler's injury puts an onus on the defense to step up.

"When your starting quarterback goes down, you never want that to happen. Again, it's football. People get hurt," Allen said. "He's going to do everything he can do to get back and help us win, and now, defensively, we've got to go out and make sure we can keep going out and getting the ball to Jimmy Clausen and the offense so they can go out and score points."